Continuously cast shape memory and super elastic alloy wires produced by a new continuous casting route

点击翻译按钮获取中文摘要

The aim of this research is development of soft copper shape-memory, super-elastic alloy material in place of the usual hard Ti-Ni alloy. The copper alloy wire with high rubber elasticity has the possibility to become the useful spring part for the industrial materials.In this research, the possibility of applying the OCC process to the fabrication of Cu-Al-Ni and Cu-Sn shape memory, super-elastic alloy wires was investigated. It was established that shape memory wires 2 mm in diameter can be continuously cast by OCC process. Cast OCC wires were found to be of single crystal or unidirectional solidified structure with a matrix phase β_1 in which γ_2 particles were precipitated in the form dendrites along the sub-grain boundaries. The γ_2 particles became fewer and the size became finer with an increase in casting speed. The Ms transformation temperature for the Cu-Al-Ni alloy and Cu-Sn alloy was in the range -19℃ to 3℃ and -55℃ to -50℃, respectively, giving rise to super-elastic behavior at the room temperature. The wires cast at slower speeds displayed shape memory attributes on heating to 90℃, whereas the wires produced at higher casting speeds exhibited super elasticity at room temperature. The Cu-Al-Ni alloy wires produced at higher casting speeds exhibited two-step super-elastic transformations as a single crystal wires. In addition, the fatigue failure of the Cu-Al-Ni alloy wires occurred after 25000 bend cycles, which was 10 times that of the conventional Ti-Ni wires. Bending properties of the OCC Cu-Al-Ni alloy wires, such as the softness and the fatigue limit, were superior to those of the conventional Ti-Ni wires.These findings suggest that the OCC process could be useful for the production of super-elastic single crystal or unidirectional solidified Cu alloy wires.